Artificial limb socket containing volume control pad

ABSTRACT

A volume control pad is provided for use in the socket of an artificial limb. The volume control pad has a core surrounded by a flexible shell. The core includes super absorbent polymer particles which form a gel upon the addition of water thereto. The volume control pad includes a tube for the introduction of water into the core portion of the pad. The volume control pad provides a simple and inexpensive means for adjusting the conformance of the socket around the residual limb from an initial swollen condition to a further point in time in which the swelling has diminished.

This application claims the benefit of Provisional application Ser. No.60/237,381, filed Oct. 4, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to the field of artificial limbs for useby individuals who have lost a limb, especially a foot, through injuryor amputation. More particularly the invention is directed toward animproved socket of an artificial limb into which the residual limb oramputation stump is mounted.

2. Background Information

Artificial limbs typically include a socket which is used to support andconnect the residual limb of a patient to the artificial limb. Theresidual limb is inserted into the socket and it is therefore desirablethat the socket should have a close fit around the residual limb toprovide a good connection between the residual limb and the artificiallimb with a minimum amount of pressure points on the residual limb. Forthis reason the sockets are custom made so that they conform to theconfiguration of the residual limb so as to be capable of supportingweight, in the case of a leg, or loading forces, in the case of an arm.

It has been found that it is highly desirable for patients to begin useof artificial limbs or prosthetic devices as soon as possible after lossof the limb through accident or amputation. If a patient can be fittedwith a prosthetic device after limb amputation, the prognosis for longterm, effective use of the prosthetic device is much higher. However, itis very difficult to obtain a good fit around the residual limb soonafter loss of the limb through amputation or accident. This is becauseof the substantial edema or swelling which takes place after the loss ofthe limb regardless of whether the loss of limb is caused by amputationor injury. The edema will continue for about two or three months untilsufficient healing has taken place which allows the fluids to bereabsorbed from the area of swelling.

Since limb prosthetic devices are most typically mounted to a patient bya socket which is customized to the configuration of the patient'sresidual limb, formation of a prosthetic socket within a few weeks oflimb amputation results in a socket which conforms to the configurationof the swollen or edema-affected residual limb. However, as the edema orswelling gradually diminishes, the initial close fit will become moreloose.

One approach for dealing with the gradual loosening of the fit betweenthe residual limb and the socket has been the addition of increasinglayers of socks over the residual limb before placing the residual limbin the socket. The additional socks are used to fill the space left inthe socket as a result of decreasing edema.

Another approach is to simply recast the socket after the edema hasdisappeared. This approach is obviously costly. Still another approachis to wait until the edema has subsided before forming the prostheticsocket. This approach, however, is undesirable because it does notpermit the amputee to obtain the therapeutic benefits associated withearly use of the prosthetic device.

The above-noted use of socks is also undesirable because the sockschange in volume with pressure, which means that the fit of the socketis dependent on the loads applied, hence the actions of the user.Another problem with such socks is loss of control, as multiple plies ofsocks allow the socket to rotate and move on the residual limb.

Several attempts have been made to manufacture a device that allows theuser to control the volume of the socket. These include air bladders andvarious types of pumping mechanisms. These devices function on apneumatic principle wherein air is used as a media to change the volume.The main problem with using air is that it is compressible and thereforethe same problems occur as with the socks.

SUMMARY OF THE INVENTION

Accordingly, it is an objective of the present invention to provide anartificial limb having a socket which provides better conformance to thepatient's residual limb.

It is also an objective of the present invention to provide the socketof an artificial limb with a simple and inexpensive means for adjustingthe conformance of the socket around the residual limb from an initialswollen condition to a further point in time in which the swelling hasdiminished.

A further objective of the present invention is to provide an apparatuswhich minimizes pain and discomfort to the patient and which can be usedwith patients who have substantial residual limb swelling or edema.

These and other objectives are achieved by providing a volume controlpad which contains a water permeable porous flexible matrix, such asopen-cell foam, having conventional super absorbent polymeric particlesin the pores or open spaces thereof (i.e., open cells in the case ofopen-cell foam). Super absorbent polymer is known in the trade as SAP.The water permeable porous flexible matrix containing the SAP issurrounded or protected by a waterproof flexible liner or shell. Forexample, the water permeable porous compressible matrix containing theSAP particles may be contained in a waterproof pouch, envelope or thelike or may be confined between waterproof layers which form part of thesocket. It is also possible to practice this invention without the SAPbeing contained in the open spaces or pores of a water permeable porousflexible matrix. For example the SAP may simply be contained within thewaterproof pouch, envelope or the like without any porous matrixmaterial being present therein. Similarly the SAP may be containedbetween the waterproof layers which form part of the socket without anyporous matrix material being present between these layers.

The volume control pad also includes means for introducing water thereinfor contact with the SAP particles so that the particles rapidly absorbthe water to thereby form a gel in accordance with known principles. Theformation of the gel greatly expands the volume of the SAP material withthe amount of volume increase depending on the amount of added water.

The volume control pad includes means for the user to periodically addwater for adjusting the volume of the pad. A flexible tube isconveniently used for the addition of water. One end of the tube isconnected to the pad so that water passing through the tube enters thecore portion of the pad which contains the SAP particles (i.e., in fluidconnection with the pad). The other end of the tube may include anyconventional valve mechanism which can be opened and closed to allow theintroduction of water when the valve is opened and to preventevaporation afterwards when the valve is closed. The terminal portion ofthe tube may also include an adapter which facilitates connection of afluid injection means such as a syringe or other type of manuallyactivated pump.

The volume control pad is advantageously placed in any desired locationin the socket. Typically the pad will be used in the same location thatconventional pressure relief formations are currently used in prostheticsockets.

The SAP particles distributed in the open cell sponge or within thepores or open spaces of other types of water permeable porous flexiblematerials, allow the gel to have highly desirable physicalcharacteristics. In particular, the gel, being composed of water andsolid polymer, is noncompressible like nongelled water. In addition thegel within the foam or other water permeable porous flexible materialbehaves like a solid and is sufficiently flexible or compliant so thatthe pad conforms to the shape of an object against which it is incontact without development of high pressure points. Thus the gel willconform to the shape of the socket located on one side and the sleeve ofthe residual limb on the other side.

In contrast, gas filled pads are undesirable because of the compressiblenature of the gas. Also, although water is noncompressible, the use ofnongelled liquids is undesirable because nongelled liquids whenintroduced into a flexible container do not behave like a solid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a preferred embodiment of the volume control pad ofthe invention.

FIG. 2 is a cross-sectional view of the control pad of the inventiontaken along line A—A of FIG. 1.

FIG. 3 is an isometric view of the volume control pad of the invention.

FIGS. 4-6 illustrate a prosthetic socket which contains a volume controlpad in accordance with the present invention.

FIG. 7 illustrates a cross-section portion of a socket showing thelocation of a volume control pad in a prosthetic socket according to anembodiment of the invention.

FIG. 8 illustrates an embodiment of the invention wherein the volumecontrol pad is bonded to the sleeve or similar structure worn over theresidual limb.

FIG. 9 illustrates an alternative embodiment of the core portion of thevolume control pad in which the open spaces for containing the SAPparticles are formed by bridging portions of the flexible shell.

FIG. 10 is a perspective cross-sectional view of FIG. 9 along line A—A.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

In a preferred embodiment the SAP particles are incorporated within thecells of an open-cell polymeric foam. The particles may be incorporatedinto the open cells of the foam during the polymeric foam formingprocess according to known techniques. Any polymeric material capable offorming open-cell foam according to known procedures may be used in thisinvention. A preferred foam is silicone foam.

Super absorbent polymer or SAP is a well known class of polymericmaterial which absorbs a large amount of water (e.g., 20 times theweight of the polymer) to form a viscous gel material. Such materialsare well known to those skilled in the art.

Super absorbent polymer is generally a water-insoluble butwater-swellable polymeric substance capable of absorbing water in anamount which is at least 10 times the weight of the substance in its dryform. In one type of super absorbent material, the material is describedchemically as having a backbone of natural or synthetic polymers withhydrophilic groups or polymers containing hydrophilic groups beingchemically bonded to the backbone or an intimate admixture therewith.Included in this class of materials are such modified polymers as sodiumneutralized cross-linked polyacrylates and polysaccharides including,for example, cellulose and starch and regenerated cellulose which aremodified to be carboxylated, phosphonoalkylated, sulphoxylated orphosphorylated, causing the SAP to be highly hydrophilic. Such modifiedpolymers may also be cross-linked to reduce their water solubility.

Super absorbent polymers are known to those skilled in the art as achemical product having an insolubilized structure as derived by asuitable method from a water-soluble polymer such as polyelectrolyte andincludes, for example, cross-lined polyacrylic acid salts, cross-linedisobutylene-maleic acid copolymer derivatives, cross-linkedstarch-polyacrylic acid salts, cross-linked polyvinylalcohol-polyacrylic acid salts, cross-linked polyvinyl alcoholderivatives, cross-linked polyethylene glycol derivatives andcross-linked carboxymethylcellulose derivatives.

Super absorbent polymers are made by conventional methods such as themethods described in the journal article “Keeping dry withsuperabsorbent polymers”, Chemtech, (September 1994) by Buchholz.

Additional examples of super absorbent polymers which are known in theart include vinyl alcohol polymers or copolymers; acrylic or methacrylicacid polymers or copolymers; sodium or potassium salts of acrylic ormethacrylic acid polymers or copolymers; and alkyl, hydroxylalkyl, orhydroxylalkyl ether esters of acrylic or methacrylic acid polymers orcopolymers. Examples of commercially available super absorbent polymersinclude Sigma-Aldrich Cat. No. 41602-9 (polyacrylic acid sodium salt);Sigma-Aldrich Cat. No. 43532-5 (polyacrylic acid potassium salt); NipponShokubai K.K., AQUALIC AS-58 (polyacrylic acid); Nippon Shokubai K.K.,AQUALIC CA (type ML-10) (cross-linked acrylic acid-sodium acrylatecopolymer); Nihon Jonyaku Co., Ltd., JURYMER AC-10L (polyacrylic acid);Nihon Jonyaku Co., Ltd., JURYMER AC-105 (polyacrylic acid); ArakowaChemical Industries, Ltd., ARASORB-F; and Sumitomo Seika Chemicals Co.,Ltd., AQUAKEEP-10SH-NF.

Further well known SAP materials are described in U.S. Pat. No.5,409,771, the specification of which is incorporated herein.

A preferred super absorbent polymer is a salt (e.g., sodium orpotassium) of cross-linked polyacrylic acid/polyalcohol graftedcopolymer. This preferred polymer is commercially available as FAVOR®SAB 800 from Stockhausen Inc. located at 2401 Doyle St., Greensboro,N.C. 27406. The FAVOR® SAB 800 super absorbent polymer has the followingcharacteristics:

-   -   Chemical basis: salt of cross-linked polyacrylic        acid/polyalcohol grafted copolymer    -   Physical form: white granules    -   Particle size: 100-850 microns    -   Product density: 540 g/l +/−30    -   Sifting properties: free flowing    -   Moisture content: 5% +/−2    -   pH value (1% gel @ 0.9% NaCl): 6.0+/−0.5    -   Storage: more than one year under dry conditions

The carboxylic groups of the FAVOR® SAB 800 super absorbent polymer aresolvated when brought into contact with water or water based liquid. Asa result, the groups partially dissociate into negatively chargedcarboxylic ions. In this state the polymer chain contains a large numberof similarly charged ionic groups which repel each other. The polymercoils become more bulky and thus extend their propensity to absorbincreasing quantities of the aqueous liquid. This process would normallylead to a complete solution of the polymer. However, due to thecross-linking between the polymer chains of FAVOR® SAB 800 superabsorbent polymer, only the formation of a gel takes place, preventingits solution. The water is strongly bonded by means of hydrogen bonds inthe gel.

Preferred foams are open-cell foams having densities from 20 to 500kg/m³ with preferred densities being in the range from 100 to 200 kg/m³.In a preferred embodiment the foam is prepared from silicone rubber suchas elastomeric silicone. The SAP is incorporated into the foamedsilicone by mixing the particles of SAP with the uncured silicone priorto foaming and curing. Thus, silicone containing an appropriate foamingand curing agent is mixed with the SAP particles and then subjected tofoaming and curing conditions to produce an open celled foam.

The foam containing the SAP particles therein constitutes the coresection of the volume control pad. The core is enclosed within aflexible shell or envelope. It is thus possible to make a volume controlpad without resorting to the use of the foam. In particular, a volumecontrol pad can be made without foam by bridging opposing portions ofthe flexible outer shell at several locations to thereby form an opencell structure within the flexible shell. In addition the SAP may simplybe incorporated within a waterproof flexible liner or shell without thecreation of a plurality of open cells therein (i.e., there being onlyone open space in the flexible liner or shell to contain the SAPtherein).

The invention will now be more particularly described by reference tothe accompanying figures.

FIGS. 1-3 show a preferred embodiment of the volume control pad used inthe present invention. The volume control pad, shown generally byreference numeral 1, includes a core 2 encased or enveloped within aflexible shell 3 which is preferably made of silicone with textilereinforcement. A core 2 of open-cell silicone foam containing SAPparticles within the cells thereof is located within flexible shell 3.According to one embodiment of the invention the core may simplycomprise a volume of space (i.e., core volume space) within the flexibleliner or shell for containing the SAP material without the presence ofthe open celled foam. A flexible silicone tube, which is attached to thepad, is in fluid communication with the core 2 for the introduction ofwater into the core so that a gel is formed within the shell. Preferablythe tube is attached to the top portion of the pad so that air withinthe core that is displaced by the addition of water, can easily bevented and removed.

Flexible tube 4 is made of conventional medical or surgical tubing suchas silicone tubing. The flexible tube 4 terminates with an adapter orcoupling device which may be used for temporarily connecting the tube toa source of water (e.g., water containing syringe or the like). Theadapter or coupling 5 includes a cap 6 which is removed when water isintroduced into the pad and replaced to prevent unwanted evaporation.

FIGS. 9 and 10 illustrate an alternative embodiment of the pad whichlacks the open cell foam. Instead of open cells provided by the foam forholding the SAP particles, the embodiment shown in FIGS. 9 and 10provide a large open cell volume by bridging or sealing opposite sidesof the flexible shell together at a plurality of locations. For example,the two sides of the shell can be fused together at a plurality oflocations 7 shown in FIGS. 9 and 10 to thereby convert the inner volumeof the flexible shell into a large open cell structure 8. Theaforementioned bridging or sealing of the opposite sides of the shellmay be omitted to thereby provide an uninterrupted volume within theshell to contain SAP particles therein.

The volume control pad is advantageously incorporated within the socketwhich is used to receive and hold the terminal portion of a residuallimb of an individual from whom a portion of the limb has been severeddue to amputation or injury. Such sockets such as the sockets describedin U.S. Pat. No. 5,972,036 are well known to those skilled in the art.The sockets to which the present invention is used generally have anopening at one end for receiving the residual limb and a cup shapedinterior which is shaped to receive the residual limb of an amputee.Typically the cup shaped interior is shaped to conform to the shape ofthe residual limb which is to be inserted therein. In particular theshaped socket is sized to conform to the shape of the residual limb uponwhich a sleeve, stocking pad, comfort liner or the like is worn. Suchsleeves, comfort liners or stocking pads are well known and are shapedof resilient material for conformation with the shape of the residuallimb.

FIGS. 4-6 illustrate a conventional socket within which the volumecontrol pad is used in accordance with this invention. As shown in FIG.4, the control pad 1 is mounted or adhered within the socket 9 at anydesirable location. For example an appropriate position for the controlpad corresponds to the positions for pressure relief formations used inthe socket described in U.S. Pat. No. 5,972,036, the disclosure of whichis incorporated herein by reference. The skilled prosthetist willunderstand how and where such pressure relief formations must beprovided in accordance with known techniques so that they can providepressure relief for sensitive areas of the residual limb during use. Thevolume control pad may be incorporated within the socket in accordancewith the procedure described in U.S. Pat. No. 5,972,036 for theincorporation of pressure relief formations in the socket.

FIGS. 4, 5 and 6 are different views of the same socket which containsvolume control pad 1 mounted therein. As shown in FIG. 5, the socket hasa posterior side 10 and an anterior side 11. The volume control pad inFIGS. 4, 5 and 6 is mounted on the posterior side 10. The tube 4 ispositioned so that the user can introduce water into the pad when theresidual limb is contained in the socket. For example, the tube may bemolded in the material which forms the socket with a portion extendingtherefrom on the outside for access by the user.

FIG. 7 illustrates an embodiment of the invention wherein the volumecontrol pad replaces the pressure relief formations described in U.S.Pat. No. 5,972,036. More particularly, FIG. 7 illustrates across-section of a portion of a socket such as the type of socketdescribed in U.S. Pat. No. 5,972,036 in which the pressure reliefformation is replaced by the volume control pad of the presentinvention. As shown in FIG. 7, the volume control pad 1 is incorporatedin the socket between wall material 12 and a smooth fabric inner linerlayer 13. The embodiment illustrated in FIG. 7 can be made according tothe technique described by U.S. Pat. No. 5,972,036 by substituting thevolume control pad of the present invention with the pressure reliefformation used in the aforementioned patent. Thus the socket illustratedin FIG. 7 corresponds to the socket described in U.S. Pat. No. 5,972,036with the exception being the replacement of the pressure reliefformation with the volume control pad of the present invention.Accordingly FIG. 7 also illustrates the inclusion of a smooth fabricouter covering layer 14 and a coupler 15.

In an alternative embodiment the volume control pad is mounted on thesleeve, comfort liner or stocking pad which the amputee wears on theresidual limb. In this embodiment the volume control pad is mounted onthe outside surface of the sleeve, stocking pad, comfort liner or thelike so that the adjustable comfort pad is situated between the sleeve,stocking pad, comfort liner or the like and the socket. This embodimentof the invention is illustrated in FIG. 8. As shown in FIG. 8 volumecontrol pad 1 is secured (for example by adhesive) to sleeve 16.

The silicone polymer used in the present invention may be any of thewell known silicone rubber or elastomer materials which are readilyavailable. Preferably the silicone should be medical grade or siliconesuitable for use in medical applications.

While the present invention has been described in terms of certainpreferred embodiments, one skilled in the art will readily appreciatethat various modifications, changes, omissions, and substitutions may bemade without departing from the spirit thereof. It is intended,therefore, that the present invention be limited solely by the scope ofthe following claims.

1. A volume control pad for use in a socket of an artificial limb; saidvolume control pad comprising a core contained in a fluid-impermeableflexible shell; a tube attached to said flexible shell in fluidcommunication with said core for the introduction of fluid into saidcore; said core comprising an open-cell foam having open cellscontaining particles of super absorbent polymer therein.
 2. The volumecontrol pad of claim 1 wherein said flexible shell, said tube or saidopen-cell foam is silicone.
 3. The volume control pad of claim 2 whereinsaid tube has a terminal end remote from said flexible shell and saidterminal end of the tube having an adapter for connection with a fluidsource; said adapter having a cap located thereon to prevent evaporationof fluid through said tube, said cap being removable to allow theintroduction of fluid into said tube.
 4. The volume control pad of claim3 wherein said super absorbent polymer comprises the salt ofcross-linked polyacrylic acid/polyalcohol grafted copolymer.
 5. In asocket for an artificial limb, said socket having a residual limbreceiving opening at one end and a cup shaped interior which is shapedto receive the residual limb of an amputee; wherein the improvementcomprises the volume control pad of claim 1 mounted in the cup shapedinterior of said socket.
 6. A method for adjusting the conformance of asocket of an artificial limb around a patient's residual limb insertedwithin said socket, said process comprising: providing a volume controlpad within said socket, said volume control pad comprising a core withina flexible shell with super absorbent polymer contained within saidcore; causing said super absorbent polymer to swell by introducing fluidwithin said core containing said super absorbent polymer so that saidsuper absorbent polymer absorbs the fluid.
 7. The method of claim 6wherein said volume control pad is provided within said socket by beingmounted within said socket.
 8. The method of claim 6 wherein said socketincludes a wall and a fabric inner liner on said wall and said volumecontrol pad is provided between said fabric inner liner and said wall.9. The method of claim 6 wherein said volume control pad is providedwithin said socket by mounting said volume control pad on a sleeve,liner or stocking pad worn on said residual limb.
 10. The method ofclaim 6 wherein said shell comprises fluid impermeable layers which formpart of said socket.